Dictionary of Chemistry [6th Ed.]

sulphuric(IV) acid 512

s

CuO(s) + H 2 SO 4 (l) →CuSO 4 (aq) +

H 2 O(l)

It is also a powerful dehydrating

agent, capable of removing H 2 O from

many organic compounds (as in the

production of acid *anhydrides). In

dilute solution it is a strong dibasic

acid forming two series of salts, the

sulphates and the hydrogensul-

phates.

sulphuric(IV) acidSee sulphurous

acid.

sulphur monochlorideSee disul-

phur dichloride.

sulphur mustard A chemical war-

fare agent, C 4 H 8 Cl 2 S; r.d. 1.27; m.p.

14.4°C; b.p. 217°C. It is a potent blis-

tering agent,Ürst used in 1915 by

Germany in World War I. It is often

known simply as mustard gas, al-

though it is an oily liquid, which can

be dispersed as an aerosol. It was one

of the early chemicals used in chemo-

therapy treatment of cancer. The sys-

tematic name is bis(2-chlorethyl)

sulphide. See also nitrogen mustard.

sulphurous acid (sulphuric(IV) acid)

A weak dibasic acid, H 2 SO 3 , known in

the form of its salts: the sulphites

and hydrogensulphites. It is consid-

ered to be formed (along with sul-

phuric acid) when sulphur dioxide is

dissolved in water. It is probable,

however, that the molecule H 2 SO 3 is

not present and that the solution

contains hydrated SO 2. It is a reduc-

ing agent. The systematic name is

trioxosulphuric(IV) acid. See also sul-

phuric acid.

sulphur(IV) oxideSee sulphur

dioxide.

sulphur(VI) oxideSee sulphur

trioxide.

sulphur trioxide (sulphur(VI)

oxide)A colourless fuming solid,

SO 3 , which has three crystalline

modiÜcations. In decreasing order of

stability these are: α, r.d. 1.97; m.p.

16.83°C; b.p. 44.8°C; β, m.p. 16.24°C;

sublimes at 50°C; r.d. 2.29; γ, m.p.

16.8°C; b.p. 44.8°C. All are polymeric,

with linked SO 4 tetrahedra: the γ-

form has an icelike structure and is

obtained by rapid quenching of the

vapour; the β-form has inÜnite heli-

cal chains; and the α-form has in-

Ünite chains with some cross-linking

of the SO 4 tetrahedra. Even in the

vapour, there are polymeric species,

and not discrete sulphur trioxide

molecules (hence the compound is

more correctly called by its system-

atic name sulphur(VI) oxide).

Sulphur trioxide is prepared by the

oxidation of sulphur dioxide with

oxygen in the presence of a vana-

dium(V) oxide catalyst. It may be pre-

pared in the laboratory by distilling a

mixture of concentrated sulphuric

acid and phosphorus(V) oxide. It re-

acts violently with water to give sul-

phuric(VI) acid and is an important

intermediate in the preparation of

sulphuric acid and oleum.

sulphuryl chlorideSee sulphur

dichloride dioxide.

sulphuryl group The group =SO 2 ,

as in *sulphur dichloride oxide.

O

O

S

Cl

Cl

sulphuryl

group

sulphur (VI) dichloride

dioxide O

Cl

Cl

sulphur (IV) dichloride

oxide

S

thionyl

group

Sulphuryl group